1. Field of the Invention
The present invention relates to pneumatic tires that enable reduction of fitting pressure, and enhancement of workability of mounting the tires to rims and durability of bead portions while maintaining a tightening force of bead cores.
2. Description of the Background Art
Bead cores for use in pneumatic tires for passenger cars are each formed by one bead wire or plural bead wires being continuously wound in a tire circumferential direction. Further, various types of bead cores are suggested in order to enhance various performance characteristics of tires. For example, a bead core in which an organic fiber is used in a part of a bead wire in order to reduce a weight of a tire (see Japanese Laid-Open Patent Publication No. 7-96720), and a bead core having formed therein a gap for absorbing vibration in order to absorb road noise (see Japanese Laid-Open Patent Publication No. 2005-335584), are suggested.
On the other hand, in recent years, flattening of pneumatic tires for use in passenger cars has been significantly restrained, and run flat tires that enable running in a punctured state have increased. Therefore, it is particularly required to enhance a tightening force of bead cores and restrain rim misalignment and rim detachment. In response to these requests, in general, a width of a bead core is increased, or the number of bead wires disposed in a bead core is increased. Thus, the tightening force of the bead core is enhanced, to restrain rim misalignment and rim detachment.
However, in a case where the tightening force of the bead core is increased, when the tire is mounted to a rim, it is difficult to move a bead portion over a hump provided in the rim, and an air pressure (hereinafter, the air pressure is referred to as “fitting pressure”) with which the tire is inflated when the bead portion is moved over the hump, is increased. Due to the fitting pressure having been thus increased, an impact becomes excessively increased when the bead portion of the tire having been moved over the hump comes into close contact with a rim flange surface. Therefore, the bead portion may be damaged, and durability of the bead portion may be deteriorated. The entire contents of Japanese Laid-Open Patent Publication Nos. 7-96720 and 2005-335584 are incorporated herein by reference.